1. Field of the Invention
The present invention relates to a globoid worm gear generating method in which tooth surfaces are ground by a tool representing an inverted conical surface.
2. Description of the Prior Art
Hitherto, as methods for generating globoid worm gears, there have been publicly known a method in which tooth surfaces of globoid worm gears (globoid worm gears having developable tooth surfaces) are ground and generated with a tool representing a plane, a method in which tooth surfaces of globoid worm gears are ground and generated with a tool representing a conical surface (see U.S. Pat. No. 4,184,796) and so on. A comparison will be made between the generating method using the plane tool and the generating method using the conical-surface tool. In the method utilizing the plane tool, the freedom of design is restricted and there exists a defect that both tooth surfaces of a worm gear cannot be generated simultaneously. Accordingly, the generating method with the use of the conical-surface tool has been widely employed at present.
This publicly-known generating method utilizing the conical-surface tool will now be described. As shown in FIG. 11, a tool 2 rotated by a motor 1 has conical surfaces. Both conical surfaces of the tool 2 simultaneously generate a globoid worm gear 3.
However, the aforesaid publicly-known worm gear generating method with the conical-surface tool 2 is not always advantageous in view of cost. This is because it take a long period of time to mill and to grind the worm gears.
A method for generating globoid worm gears with a milling cutter of an inverted conical shape has been proposed (see Japanese Patent Unexamined Publication No. 2-232119).
This method will be explained with reference to FIG. 12. Rotation of a motor 11 is transmitted to a holder 14 by means of a pulley 12 and a belt 13. A cutting tool 15 for milling is attached to the holder 14. The cutting tool 15 cuts a globoid worm gear 16 when the holder 14 is rotated.
Such method of cutting the globoid worm gear 16 by the cutting tool 15 of the inverted conical shape, has an advantage that a period of time required for cutting is shortened. However, the tooth surface of the gear is rough because of the cutting by means of the cutting tool 15, so that there arises a necessity of finish-grinding the surface with a grindstone. Normally, a difference between a contour of a conical grindstone gear made of a conical-surface grindstone for the finish-grinding and a contour of the threaded gear produced by the cutting tool of the inverted conical shape is large so that a grinding stock is increased. As a result, a period of time of grinding for finishing the surface of the gear disadvantageously becomes longer after all.
In view of the above, an object of the present invention resides in providing a novel method for generating globoid worm gears by which the gears can be generated in a short period of time.